Liquid separation by zeolite membranes

ABSTRACT

Apparatus for removing water from water containing liquids in which a chamber with walls formed from a zeolite membrane can be immersed in the liquid mixture so that water passes into the interior of the chamber where it can be removed.

The present invention relates to an apparatus and a method for theremoval of water from liquids, such as organic liquids, biologicalfluids, foodstuffs, pharmaceutical preparations etc. more particularlyit relates to a non-distillation method of removing water from liquidsin order to obtain a substantially dry liquid.

In chemical operations it is sometimes necessary to have substantiallydry liquids e.g. as solvents, reagents etc. For some liquids it is verydifficult to obtain them in a substantially dry state as, for exampleazeotropic mixtures are formed on distillation and the removal ofresidual amounts of water can involve difficult and expensive processessuch as re-distillation with another organic liquid. These processes caninvolve the use of harmful chemicals such as benzene and cyclohexane.Other liquids would be degraded thermally by the temperatures requirefor effective removal of water.

A particular requirement is for the supply of substantially dry liquidsfor small scale or laboratory use where the liquids need to be storedfor a period and the cost of these liquids can be very high.

In the laboratory organic solvents can be left some while before beingused and are prone to absorb water from the atmosphere unless strenuousprecautions are taken to prevent this.

We have now devised an apparatus and a process which can dehydrateliquids in situ on a small scale without the need for distillationparticularly with thermally sensitive compounds.

According to the invention there is provided apparatus for the removalof water from a water-containing liquid, which apparatus comprises areceptacle for the water-containing liquid, a membrane zeolite membranewhich can contact the water-containing liquid in the receptacle and awater removal means for removing water separated by the zeolitemembrane.

The invention also comprises a chamber at least part of the walls ofwhich comprise a zeolite membrane which has an outlet from which watercan be removed. In use the chamber is immersed in the liquid containingwater so that only the water can pass into the chamber and thus beseparated from the liquid.

There can be a plurality of chambers interconnected to give a largersurface area of zeolite. The chambers can be connected by means of atube or the like, which leads out of the liquid into which the chamberis immersed.

The zeolite membrane includes zeolitic membranes and membranes made fromzeo-type materials.

Zeolitic membranes and membranes which incorporate zeolites are alsowell known and can come in a range of different types. European PatentApplication 0481660 discloses and discusses prior art zeo-type membranesand refers in particular to U.S. Pat. Nos. 3,244,643, 3,730,910 and4,578,372, Applied Catalysts 49(1989) 1-25, DE-A-3827049, CA1235684,JP-A-63287504, JP-A-63291809, EP-A-180200, EP-A-135069.

Zeo-type materials are also known as molecular sieves which are widelyknown and used. They comprise an extended network of channels formedfrom silicon/oxygen tetrahedrons joined through the oxygen atoms.Zeolites and alumino-silicates are the most commonly known form ofzeo-type materials and the present invention is applicable to anymembrane formed from zeo-type materials and particularly applicable tozeolites and alumino-silicates. In the "Atlas of Zeolite StructureTypes", Meier and Ofsen, 1987, Polycrystal Book Service, Pittsburg USA,various types of structure are described and, for example, thosedescribed as having LTA, MEL, MFI or TON structure can be used.

In "New Developments in Zeolite Science and Technology Proceedings ofthe 7th International Conference, Tokyo, 1986, page 103, another classof zeo-type materials are disclosed as crystalline aluminophosphate,silicoalumina phosphates and other metallo-alumino phosphates.

The zeolite membranes are preferably in the form of zeolite crystalsgrown or deposited on a porous support.

The porous supports on which zeo-type membranes are formed and which canbe used in the present invention include those formed of metals,ceramics, glass, mineral, carbon or polymer fibres or cellulosic ororganic or inorganic polymers. Suitable metals include titanium,chromium and alloys such as those sold under the Trade Marks "Fecralloy"and "Hastalloy" and stainless steels. The porous supports are preferablyformed of a mesh or from sintered metal particles or a mixture of both.These are commonly sold in the form of filters.

Porous ceramics, glass mineral or carbon materials can also be usedincluding porous silicon and other carbides, clays and other silicatesand porous silica.

If desired, the support can be a zeolite formed by compression or usinga binder. The shape of the support is not critical, for example, flatsheet, tubular, wound spiral, etc. can be used. If polymeric materialsare used, these can optionally be film coated with metal or metal oxideor a silicic acid as herein defined. The porous support can be also be agranular solid e.g. formed of particles of a closely packed materialsuch as a pellitised catalyst.

The present invention can be used with porous supports of any suitablesize although, for large flux rates through a membrane, large pore sizesare preferred. Preferably pore sizes of 0.01 to 2,000 microns, morepreferably of 0.1 to 200 and ideally of 1 to 20 microns are used. Poresizes up to 300 microns can be determined by bubble point pressure asspecified in ISO 4003. Larger pore sizes can be measured by microscopicmethods.

The zeolite membranes which can be used in the present invention arethose with a pore size which will effectively trap the molecules of theappropriate size and zeolite membranes of pore size of 3 to 15Angstroms, and more preferably of 3 to 5 Angstroms can be used in manycases.

The zeolite membranes should be substantially free of defects so as toprovide an effective separation and zeolite membranes as described inour co-pending application PCT/GB95/02221 can be used.

In one embodiment of the invention the chamber can be formed from atleast two substantially flat spaced apart zeolite membranes joined attheir perimeters and the hollow tube passes through and is connected tothe inside of the chamber.

In a particular embodiment of the invention membranes are mounted inpairs so as to define a closed space between, and bounded by the pair ofmembranes. The interior of this space is connected to the inside of ahollow tube on which the membranes are mounted, so that fluid passingthrough the membrane can be led away through the hollow tube. Forexample each membrane in a pair can be in the form of a plate or thelike e.g. in the form of discs, which are spaced apart from the eachother with their outside edges connected and sealed together. The hollowtube passes through the membranes and, where it passes through each ofthe membranes, it is sealed against the membrane. Thus the interior ofthe tube is connected to the space between the membranes in the membranepair so as to provide an enclosed space bounded by the membranes and theinterior of the tube.

The capacity of the apparatus is determined mainly by the capacity ofthe membrane and a series of membranes can be placed in parallel toobtain a larger capacity and throughput.

In another embodiment of the invention the membranes are tubularmembranes and one or more tubular membranes can be positioned so thatwhen they are placed in a liquid in a receptacle, water can pass throughthe membrane where it can be removed leaving the liquid with a reducedwater content in the receptacle

In use, the water-containing liquid enters the apparatus through aninlet, passes over the zeolite membrane where water is separated fromthe liquid and the water is removed via the water removing means and theliquid from which the water has been removed passes out through theliquid outlet. The invention also comprises a method for the removal ofwater from water-containing liquid which method comprises passing thewater-containing liquid over a zeolite membrane in the apparatus of theinvention and removing the water removed from the water-containingliquid and recovering the liquid from which the water has been removed.

The invention has advantages in removing water from liquids where it isnot possible or practical to remove water by means of distillation orother conventional means, for example by reverse osmosis. The inventioncan be used for the removal of small amounts of water in situationswhere other methods have great difficulty in removing the water.

Preferably the water separated is removed by reducing the pressure atthe water removing means to draw off the separated water from themembrane and causing more water to enter into the membrane from thewater-containing liquid and thus having a continuous or semi continuoussystem.

If necessary the liquid from the outlet can be passed through theapparatus again to obtain a further dehydration or more than oneapparatus can be placed in series to obtain a sequential dehydration.

In laboratory or small scale use preferably there is a means such as apump for pumping the water-containing liquid through the apparatus andsome means of reducing the pressure at the water removing means. In oneembodiment a motor which operates a pump at the water-containing liquidinlet and a suction pump as the water removing means is provided so thatin operation the water-containing liquid feed is attached to the inletthe motor turned on and the water removed to obtain at the outlet aliquid with a lower water content.

If desired the motor need not be provided and the pump and suction meanscan be operated by any external power source e.g. from a water supply inthe same way as a laboratory vacuum pump.

Advantageously the liquid is stirred e.g. by means of a stirrer such asa magnetic stirrer.

In order to facilitate the effectiveness of the method of the presentinvention the various liquid streams to and from the apparatus can beheated or cooled as appropriate depending on whether the process ofremoving the water is exothermic or endothermic and whether vapours areformed or are present. Optionally heat-exchangers can be provided tofacilitate this heating or cooling process.

In some applications the water passes through the membrane in the formof water vapour and, as the absorption of the latent heat of evaporationof the water is an endothermic process, there is preferably a heatingmeans to maintain the temperature of the liquids.

It is a feature of the invention that it does not require large amountsof energy and/or a very high vacuum to remove the water, as is the casein distillation and vacuum distillation, or high pressures as in thecase of reverse osmosis, but it can be used to supply small amounts ofdehydrated liquids "on demand" so as to prevent contamination arisingfrom the storage of dehydrated liquids. Thus by the use of the apparatusand method of the invention it is possible to purchase organic liquidsof commercial quality, which can incorporate small amounts of water and,as required, produce substantially dry liquids from these, or to recyclesolvents.

Although the apparatus has been described with reference to theseparation of water from water containing liquids it can be used toseparate any two liquids where only one liquid can pass through thezeolite membrane.

The invention is illustrated in the accompanying drawings in which

FIG. 1 is a diagrammatic representation of an apparatus according to theinvention

FIG. 2 is an illustration of the apparatus of the invention and

FIG. 3 is an enlarged view of a membrane of FIG. 2 and

FIG. 4 is an alternative arrangement of the membrane.

Referring to FIG. 1 a container (1) has an inlet for water-containingliquid (2) which leads to a membrane containing receptacle (3) whichcontains a zeolite membrane. From (3) there is an outlet (4) which takesthe treated liquid stream to a conditioning container (5) and thence touse.

Water removing means (8) leads water separated by the zeolite membraneto an outlet. Pipes (6) and (7) act as a heat exchanger and are capableof passing heating or cooling liquid around the (3) to maintain it atthe correct temperature.

In use the water-containing liquid is passed through (2) to (3) by meansof the application of an external pressure e.g. by a pump. Low pressureis applied at (8) to remove water separated by the zeolite membrane. Thetreated liquid from (3) can be passed through conditioning chamber (5)if needed e.g. to adjust the temperature of the liquid so it is suitablefor its immediate purpose or for any other purpose.

If needed to heat or cool (3), heating or cooling liquid can be passedthrough pipes (6) and (7) as appropriate.

Referring to FIG. 2, a receptacle (10) contains the liquid from whichwater is to be removed. A hollow tube (11) has zeolite membrane chambers(12), shown in more detail in FIG. 3, attached to it. There are meansattached to tube outlet (14) to remove water and water vapour from thetube (11). There is a nitrogen feed (15) which generates a blanket ofnitrogen under pressure over the liquid surface. There is a heater (16)which can maintain the liquid at the desired temperature and a magneticstirrer (17) which can stir the liquid in the receptacle (10). There aremeans (not shown) to add and remove liquid from the receptacle.

Referring to FIG. 3 the zeolite chamber (12) is a structure formed fromtwo wire mesh supports (12a) and (12b) on which are deposited orcrystalised zeolite membranes

The ends (17) of each of the membranes are joined together to form asubstantially air tight seal. Where the tube (11) passes through themembrane it is joined to the membrane to form a substantially air tightseal at (19).

In use the liquid containing the water is placed in receptacle (10) andthe vessel sealed. Nitrogen under pressure enters through feed (15) anda vacuum is applied at (14). The heater (16) is turned on and stirrer(17) operated.

Water passes through the membrane into chamber (12) and into tube (11)where it can be removed; the liquid in the receptacle then has a loweredwater content. When the water content has been reduced to the requiredlevel the liquid can then be removed.

Referring to FIG. 3 tubes (23) are made of metal mesh and have a lowerportion (24) on which is deposited a zeolite membrane, the tubes areconnected to a manifold (26) and a vacuum is applied at (25). Water isdrawn through membranes (24) into the tubes, from where it can beremoved via (25).

The equipment thus enables liquid to be at least partially dehydrated asrequired in an easy and convenient manner.

What is claimed is:
 1. An apparatus for removing water from a watercontaining liquid in which the water containing liquid is contacted witha zeolite membrane and water passes through the membrane, whichapparatus comprises a receptacle for the water containing liquid, inwhich receptacle is placed a plurality of interconnected chambers eachof which chamber comprises two spaced apart zeolite membranes, joined attheir edges to form the chamber, the interior of each chamber only beingaccessible to liquid in the said receptacle by liquid passing throughthe zeolite membrane, each chamber being mounted around aninterconnecting hollow tube passing through the chambers and eachchamber having a linear dimensions substantially greater than thedistance apart of the spaced apart zeolite membrane forming the chamber,so as to form a structure comprising a plurality of substantiallyparallel chambers mounted around the interconnecting tube whereby whenthe chambers are placed in a water containing liquid in the saidreceptacle water is passed through the said membrane into the chamberand is able to be removed through said interconnecting hollow tube. 2.Apparatus as claimed in claim 1 in which there are means attached to thesaid outlet to remove water and water vapor through the saidinterconnecting hollow tube and there is a nitrogen feed adapted togenerate a blanket of nitrogen under pressure over the surface of aliquid in the receptacle.
 3. Apparatus as claimed in claim 2 in whichthe zeolite membrane is formed by the deposition of zeolite crystals onto a wire mesh.
 4. Apparatus as claimed in claim 3 in which the zeolitemembrane has a pore size of 3 to 15 Angstroms.
 5. Apparatus as claimedin claim 4 in which the zeolite membrane has a pore size of 3 to 5Angstroms.
 6. Apparatus as claimed in claim 1 in which the zeolitemembrane has a pore size of 3 to 15 Angstroms.
 7. Apparatus as claimedin claim 2 in which the zeolite membrane has a pore size of 3 to 15Angstroms.
 8. Apparatus as claimed in claim 1 in which the zeolitemembrane is formed by the deposition of zeolite crystals on to a wiremesh.
 9. Apparatus as claimed in claim 8 in which the zeolite membranehas a pore size of 3 to 15 Angstroms.
 10. Apparatus as claimed in claim9 in which the zeolite membrane has a pore size of 3 to 5 Angstroms. 11.A method of separating water from a water containing liquid by using anapparatus which comprises a receptacle for the water containing liquidand a plurality of interconnected chambers each chamber comprising twospaced apart zeolite membranes joined at their edges and being mountedaround an interconnecting hollow tube, and wherein the method comprisesimmersing the interconnected chambers in the water containing liquid sothat only the water from the water containing liquid passes through thezeolite membrane into the interior of the chambers and the seperatedwater is removed from the chambers through the interconnecting hollowtube.